Disable heap debugging on Windows by default

Windows heap debugging negatively impacts the performance of the debuggee (check out the attached clips to get a rough idea how much).

According to Microsoft, there is a diminishing return from having it enabled as the C Runtime Library embeds memory checks anyway (see their Dev Blogs). It has been thus disabled by default in both Visual Studio and Visual Studio Code.

Heap debugging is normally controlled via _NO_DEBUG_HEAP environment option. CDB has additionally a command line option: -hd. LLDB has no special options but seems to respect _NO_DEBUG_HEAP environment variable.

Here's what's going on in the clips:

• locating a file in a project by typing its name
• scrolling to line 100
• jumping to line 200 using the locator
• jumping through some menus

With heap debugging disabled the whole sequence takes ~25 sec - about the same time it takes for only the locator to show up first time if heap debugging is enabled.